This question comes up a lot, especially in winter when energy bills start climbing. Whether it’s cheaper to heat one room or the whole house depends on how your heating system is set up and how well the rest of the house retains warmth.
In theory, heating one room should cost less. In practice, central heating systems aren’t always designed to work that way. Closing radiators can affect circulation and cause the boiler to run less efficiently, which reduces the expected savings.
Where single-room heating works best is when the rest of the house is reasonably sealed. Cold air from unused rooms can otherwise flow into the heated space, forcing the system to work harder to maintain temperature.
This worked better than expected once airflow between rooms was reduced and unused spaces weren’t acting as cold reservoirs.
This balance between targeted heating and overall heat retention is covered in more detail in the main WarmGuide overview.
If one room always struggles, this guide and this one help explain why.